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I try to use an MicroSD card containing a chroot environment which I can break, e.g. by installing software, without damaging the OS on my bq Aquaris E4.5 Ubuntu Edition, however I can not let the filesystem being auto-mounted and use the chroot at the same time.

  • ext4 and similiar filesystems do not get mounted by ciborium → by default the sd card is not mounted when using ext4, an error is indicated and I am asked to format the disk as vfat
  • vfat does not support the execute permission → I cannot run programs of the chroot when the chroot is saved on a vfat partition
  • To me there is no known way to start a script automatically on startup (I have found this while searching for an answer) without changing the file-system which is by default intentionally mounted as read-only → I can not easily create a mount script executed on startup

So I wonder whether there is a way to auto-mount an MicroSD-card which can be used to store an chroot without modifying the write-protected parts of the phone.

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You can call to the script in /etc/rc.local. But previously you need remount loop0 like rw because it is only read. (sudo mount /dev/loop0 / -o remount, rw) – Gelux Jun 9 '16 at 8:34
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I have ext2 partition on my sd card and I want automount for this partition. Here is my solution for Ubuntu Touch BQ Aquaris m10.

At first, we make a system partition writable:

sudo touch /userdata/.writable_image

After doing this system will reboot. Then, we edit /lib/init/fstab:

sudo nano /lib/init/fstab

and add this string in bottom:

/dev/mmcblk1p2  /home/phablet/mnt/sd      ext2            defaults,noatime,nodiratime,errors=remount-ro 0 2

Then, we make system partition read-only again:

sudo rm /userdata/.writable_image

And rebooting:

sudo shutdown -r now

It works!

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I haven't tested it, but it requires changing the root fs. As far as I have read, this is discouraged beacause it can lead to undefined behaviour in case of updates - a reflash of the device might become necessary, and I would prefer to avoid that case. So I do not want to change my root fs - there is a reason why it is read-only. – paulusASol Dec 4 '16 at 20:19
    
Some changing in rootfs can be done without problems. Please, read carefully comments before answer and the answer of Larry Price in this topic concerning it. Larry (as far I understand) is from Canonical Team. – Vladimir Dec 5 '16 at 2:37

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